Effect Of Water-Rock Interaction And Sulfur Deposition On Mining Dynamics Of Acid Gas Reservoir

In the process of acid gas reservoir exploitation,as the temperature and pressure decrease,the solubility of elemental sulfur in the gas reservoir changes,and the precipitated elemental sulfur changes the pore structure of the reservoir,which reduces the porosity and penneability of the fonnation.At the same time,due to the pressure decline of the temperature,the bottom water intrusion reacts with the acid gas in the original gas reservoir to form an acid liquid,which reacts with the reservoir minerals and has a certain improvement effect on the porosity and permeability.However,the impact of the combined effects of the two on the reservoir is unknown.This paper has carried out research on this point.I hope to provide some guidance for the development of acid gas reservoirs in the future.The results of the research are as follows(1)The mechanism of acid gas-water-rock reaction:acid gas is dissolved in formation water and reacts with carbonate minerals.The dissolution rate of the mineral is expressed by the rate of change of the concentration of the components in the solution,and a reaction rate model is established.In order to study the influence of water-rock reaction on reservoir physical properties,the mineral particles are simplified into regular spheres,and the change of porosity is characterized by the radius of mineral particles to determine the rate of change of porosity.(2)Research on reservoir damage caused by sulfur deposition:According to the investigation,the elemental sulfur in the gas reservoir is mainly precipitated physically,that is,by its solubility in acid gas.On the basis of previous studies,the example calculation is based on the plane radial flow.It is found that the reduction of reservoir porosity and permeability caused by sulfur deposition is related to wellbore distance,pressure,and production.The closer the wellbore,the higher the pressure,and the higher the production,lead to the greater the sulfur saturation,as well as the more serious the damage of the porosity and permeability of the reservoir.(3)Experimental study on water-rock reaction and sulfur deposition:The high temperature and high pressure reactor experiment for water-rock reaction and the displacement experiment for sulfur deposition were carried out with reaction time and pressure as variables.A total of two groups of experiments,seven cores,a group of experiments under different reaction time at 50MPa,the results show that the core porosity and permeability have a small reduction.The other group reacted for 72 h under different pressures.The experimental results show that the core pore permeability decreases when the pressure is 50 MPa and 40 MPa,and the porosity and permeability increase when the pressure is 30 MPa and 20 MPa.(4)Combining the effects of water-rock reaction and sulfur deposition on reservoir physical properties,the influence of the two interactions on formation porosity and permeability is established,and the calculation is based on the plane radial flow.The calculation results show that the reservoir porosity and permeability change are different under different pressures,radial distances and yields.Based on the influence of water-rock reaction and sulfur deposition on reservoir permeability,the gas well productivity at several production time points was calculated.The calculation results show that the production capacity has increased in the early stage and began to decline in the later stage.